Fix significant figure rounding - #390
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The issue is in the FormattedBigUint::Display implementation in core/src/num/biguint.rs. Currently, when formatting to a specific number of significant figures (sf_limit), the code truncates the string and replaces the remaining characters with '0'. This causes 666 to drop down to 660 without checking if the truncated portions should instead cause the value to round up (which would correctly make it 670). To fix this, we need to round the string based on the least significant kept digit before filling the rest with zeroes. However, there's another structural problem: FormattedBigUint currently stores base: Option<Base>, meaning that when write_base_prefix is false, the base information is lost, which would break rounding for bases other than 10 (since we wouldn't know the correct threshold for "halfway" to round up). We will change FormattedBigUint to always remember its Base.
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The issue is in the FormattedBigUint::Display implementation in core/src/num/biguint.rs. Currently, when formatting to a specific number of significant figures (sf_limit), the code truncates the string and replaces the remaining characters with '0'.
This causes 666 to drop down to 660 without checking if the truncated portions should instead cause the value to round up (which would correctly make it 670).
To fix this, we need to round the string based on the least significant kept digit before filling the rest with zeroes.
However, there's another structural problem: FormattedBigUint currently stores base: Option, meaning that when write_base_prefix is false, the base information is lost, which would break rounding for bases other than 10 (since we wouldn't know the correct threshold for "halfway" to round up).
We will change FormattedBigUint to always remember its Base.
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